1. Field of the Invention
The present invention relates to a thin composite noise absorption product which is characterized by high noise reduction, high rigidity and high strength. More particularly, it relates to a composite noise absorption product formed with a hard board of a fiber web and a thermoplastic resin.
2. Description of the Prior Art
Soundproofing devices such as soundproofing walls are widely used to reduce the noise level in offices, houses, apartments, etc. Various materials have been used as the noise absorber in such soundproofing constructions. Very often, inorganic fibrous materials, such as glass fiber asbestos and ceramic fibers, have been widely used in the form of mats, cloths or the like for this purpose. Conventional noise absorption products are prepare by bonding the fibers with a small amount of a binder to form a mat or a cloth having a plurality of coarse voids between fibers to provide high noise absorption characteristics. These noise absorption products are usually used in combination with sound insulating materials, such as metals, plastics, concrete or the like. However, these conventional noise absorption products made of a bonded fiber web have significant disadvantages. For one, they are characterized by low rigidity, low strength and are bulky. Accordingly, it is difficult to fabricate a thin hard board as a noise absorption product or to mold the material into certain shapes, such as that of a three dimensionally surfaced board.
As a result, it is necessary to use a yoke or a frame for construction of a soundproofing wall or the like. Moreover, the coarse voids between the fibers of these conventional bonded fiber webs produce products having a high water absorption property. When water is absorbed and the voids are filled, the noise absorption characteristics are greatly decreased. Moreover, it is difficult to remove the water. Accordingly, it is not advantageous to use such a bonded fiber web as a noise absorption product outdoors under conditions where exposure to water, such as from rainfall, is likely. Another disadvantage is that these conventional bonded webs have low adhesive strength and are easily deformed since the amount of the binder in the bonded fiber web is small. Furthermore, when the bonded fiber web is wet or has been exposed to sunlight for a long period of time, the binder becomes deteriorated and the fibers loosen, deforming the product. Consequently, there exists a need for an improved soundproofing material.